FIG. 1 is a schematic functional block diagram illustrating a typical optical disc drive. The optical disc drive 100 has an optical pickup head (PUH) 10. An optical disc 110 having a center hole is placed on a turn table 122. The turn table 122 is driven to rotate by a spindle motor 120 such that the optical disc 110 is rotated with the turn table 122. There are two mechanisms for moving the optical pickup head 10 in a tracking (radial) direction. The first mechanism drives long-distance movement of a sled 14 by a sled motor 130. The second mechanism drives tiny movement of a lens 12 by a tracking coil 140. In addition, the lens 12 is driven to move in the focusing direction by a focusing coil 145 to perform a focusing operation. Generally, the optical pickup head 10 has several laser diodes for reading data from corresponding types of optical discs. For example, the optical pickup head 10 includes a CD laser diode (780 nm wavelength), a DVD laser diode (650 nm wavelength) and a blue-ray laser diode (405 nm wavelength).
When a weak electronic signal is generated in response to an optical signal reflected from the optical disc 110 and received by the optical pickup head 10, the electronic signal is transmitted to a radio frequency (RF) amplifier 150. By the RF amplifier 150, the electronic signal is processed into a sub-beam addition signal SBAD, a radio frequency signal RF, a tracking error signal TE and a focusing error signal FE. These signals SBAD, RF, TE and FE are further processed by a back-end digital signal processor (DSP) 170. According to the changes of the tracking error signal TE and the focusing error signal FE outputted from the digital signal processor 170, a first motor driver 160 generates three driving signals to drive the sled motor 130, the tracking coil 140 and the focusing coil 145, thereby properly positioning the optical pickup head 10 at the desired track and desired focusing position. The driving signal generated by the first motor driver 160 for driving the tracking coil 140 to move the lens is also called as a tracking output signal TRO. Moreover, under the control of the digital signal processor 170, a second motor driver 165 drives the spindle motor 120 to rotate, thereby permitting rotation of the disc 110 at a proper rotating speed.
After an optical disc is loaded into the optical disc drive, a start-up procedure is performed to realize the type of the optical disc. The common type of optical disc includes a compact disc (CD), a digital versatile disc (DVD) or a blue-ray disc. After the type of the optical disc is realized by the optical disc drive, associated controlling parameters are acquired to access the optical disc.
For example, the conventional optical disc drive may identify the type of the optical disc according to the distance between a surface layer and a data layer of the optical disc. FIGS. 2A and 2B are schematic diagrams illustrating associated detected signals when the loaded optical disc is a digital versatile disc and a compact disc, respectively.
As shown in FIG. 2A, the distance between the surface layer and the data layer of the digital versatile disc 200 is 0.6 mm. In a case that the focusing coil of the optical disc drive is controlled to have the lens 202 move toward the digital versatile disc 200, the focusing point of the light beam successively crosses the surface layer and the data layer. When the focusing point crosses the surface layer, the amplitude of the radio frequency signal RF has a smaller peak value. When the focusing point crosses the data layer, the amplitude of the radio frequency signal RF has a larger peak value. In addition, when the focusing point crosses the surface layer, the S curve of the focusing error signal FE has a larger peak-to-peak value. Whereas, when the focusing point crosses the data layer, the S curve of the focusing error signal FE has a smaller peak-to-peak value. Like the radio frequency signal RF, the timing waveform diagram of the sub-beam addition signal SBAD also has two peak values.
As shown in FIG. 2B, the distance between the surface layer and the data layer of the compact disc 200 is 1.2 mm. In a case that the focusing coil of the optical disc drive is controlled to have the lens 202 move toward the compact disc 250, the focusing point successively crosses the surface layer and the data layer. Similarly, the radio frequency signal RF has two different peak values when the focusing point crosses the surface layer and the data layer. In addition, the S curve of the focusing error signal FE has two different peak-to-peak values.
Please refer to FIGS. 2A and 2B again. Assuming that the speed of moving the lens 202 is constant, the distance between the peak values of the radio frequency signal RF for the compact disc is greater than the distance between the peak values of the radio frequency signal RF for the digital versatile disc. Similarly, the distance between the S curves of the focusing error signal FE for the compact disc is greater than the distance between the S curves of the focusing error signal FE for the digital versatile disc. According to these characteristics, the loaded optical disc is determined as a compact disc or a digital versatile disc.
However, if the speed of moving the lens is instable, the possibility of erroneously identifying the compact disc and the digital versatile disc will be increased. For enhancing the identification success rate, the method described in U.S. Pat. Nos. 7,149,169 or 7,161,886 further includes an identifying step. In addition, the loaded optical disc is determined as a compact disc or a digital versatile disc according to the sub-beam addition signal SBAD.
In U.S. Pat. No. 7,161,886, different laser diodes are turned on when the lens is moved in different directions, and the loaded optical disc is determined as a compact disc or a digital versatile disc according to the relationship between the radio frequency signal RF and the focusing error signal FE.
The above methods are used for determining whether the loaded optical disc is a compact disc or a digital versatile disc. Generally, the compact disc and the digital versatile disc are classified as non-blue-ray discs.
As the new generation blue-ray discs are introduced to the market, it is important to immediately determine whether the loaded optical disc is a compact disc, a digital versatile disc or a blue-ray disc during the start-up procedure.
FIGS. 3A-3C are schematic diagrams illustrating three types of optical discs. FIGS. 3D-3E are schematic diagrams illustrating the method for determining whether the loaded optical disc is a blue-ray disc or a non-blue-ray disc according to the prior art. This method is described in US Patent Publication No. US 2006/0104176. This method may identify the type of the loaded optical disc according to a working distance of the lens and a distance between a data layer and a surface layer of the optical disc. As shown in FIG. 3A, the blue-ray disc 310 has a thickness of 1.2 mm. A distance between the data layer 313 and the surface layer 311 of the blue-ray disc 310 is 0.1 mm. As shown in FIG. 3B, the digital versatile disc 330 has a thickness of 1.2 mm. A distance between the data layer 333 and the surface layer 331 of the digital versatile disc 330 is 0.6 mm. As shown in FIG. 3C, the compact disc 350 has a thickness of 1.2 mm. A distance between the data layer 353 and the surface layer 351 of the compact disc 350 is 1.2 mm.
As known, since the blue light source of the optical pickup head works with a high numerical aperture (NA) lens and generates short-wavelength light beams, the lens has a short focal length. In this circumstance, the working distance of the blue-ray disc is smaller than the distance between the surface layer and the data layer of the digital versatile disc or the compact disc (i.e. smaller than 0.6 mm). Generally, the working distance is an allowed moving distance of the lens of a blue-light optical pickup head toward the optical disc.
As shown in FIG. 3D, when the blue laser diode radiates light onto the blue-ray disc 310 and the focusing point is moved within the working distance, two reflection signals are generated because the focusing point crosses the surface layer 311 and the data layer 313 of the blue-ray disc 310, respectively. The first reflection signal 381 is obtained from the reflection of the surface layer 311 of the blue-ray disc 310. The second reflection signal 382 is obtained from the reflection of the data layer 313 of the blue-ray disc 310.
On the other hand, as shown in FIG. 3E, when the blue laser diode radiates light onto the digital versatile disc 330 and the focusing point is moved within the working distance, only a reflection signal 383 is generated. Since the distance between the data layer 333 and the surface layer 331 of the digital versatile disc 330 is 0.6 mm, the reflection signal 383 is obtained from the reflection of the surface layer 331 of the digital versatile disc 330. In other words, since the focusing point of the blue laser light fails to reach the data layer 333 of the digital versatile disc 330, no other reflection signal is generated. Similarly, only one reflection signal is detected when a compact disc is loaded.
As such, the loaded optical disc is determined as a non-blue-ray disc (e.g. a compact disc, a digital versatile disc) or a blue-ray disc according to the reflection signal number. If two reflection signals are generated, the optical disc is determined as a blue-ray disc. Whereas, if only one reflection signal is generated, the optical disc is determined as a non-blue-ray disc (e.g. a compact disc, a digital versatile disc).
As know, the blue laser diode is very expensive. Since the blue laser diode needs to be turned on to identify the type of the optical disc once the optical disc is loaded into the optical disc drive, the use life of the blue laser diode will be shortened. Moreover, since the working distance of the blue laser light is very short, the lens and the optical disc are possibly abraded by each other when the lens is moved to identify the type of the optical disc.